A certain number of devices used for the positioning and orientation in space of various members with respect to any base are already known. By way of examples isostatic devices of the tri-bipod type or Stewart platforms can be cited. The latter consist of six struts of adjustable length connecting the member to be positioned and to be oriented on the base. These six adjustable lengths provide six degrees of freedom corresponding to three position coordinates and three position angles. The essential properties of these devices are the precision of the adjustment able to be obtained, the amplitude of the adjustment field, and their stiffness.